The present invention relates to illumination devices. More particularly, the present invention relates to illumination devices provided with a plurality of light-emitting devices which includes in a resin case a light emitter excited by light from a light-emitting element, and which seals the light-emitting element within this resin case.
A light source for some illumination devices is a light-emitting diode (hereinafter referred to as “LED”) serving as a light-emitting element. The illumination device of this type achieves higher output through light distribution control with a reflection plate or a lens for the purpose of obtaining high illumination intensity.
Frequently, such an illumination device includes a plurality of LED packages arranged on a substrate or a plurality of LED elements loaded within an encapsulated LED package as known to one of skill in the art.
Moreover, some illumination devices achieve a higher light output by performing light distribution control with a lens or a reflection plate when light distribution of an LED itself is wider than a desired light distribution.
Here, an LED of white or equivalent light bulb color used in the illumination device has an LED element which usually emits blue light (light in a wavelength range of approximately 380 to 480 nm) and which is sealed with an enclosure such as a phosphor-containing resin case made of silicon or epoxy, for example. With this illumination device, a part of the blue light excites a light-emitter included in the resin case to be converted into light in a wavelength of approximately 480 to 780 nm, while the rest of the blue light remains unconverted and transmitted through the resin case. Through the combination of light in a wavelength range of approximately 480 to 780 nm with the unconverted blue light in a wavelength range of approximately 380 to 480 nm, conversion into a desired color (for example, white) in the illumination device is made.
For the LED, a visible tint varies depending on an irradiation direction of the LED. For example, a white LED appears bluish-white in the vicinity of a center of the irradiation surface and appears more yellowish with distance from the center, so that a yellow ring appears at an outer circumference in some cases. Problems of color unevenness particularly arise in the event where a proximity position is irradiated by an illumination device provided with a white LED.
It may further be assumed that when a reflection plate or a lens is used for obtaining high illumination intensity, or when an LED (for example, an LED package loaded with a plurality of LED elements) with a large light-emitting portion is used, a problematic appearance of color unevenness becomes prominent.
In the first case where reflection plates or a lens are used, one possible countermeasure is subjecting the reflection plate or the lens to diffusion processing. However, this has led to a decrease in light extraction efficiency.
Moreover, using a reflection plate or a lens subjected to diffusion processing in the LED with a large light-emitting portion requires a very large lens or a reflection plate, thus resulting in failure to achieve a compact illumination device.